Method of transmission for protection of data reproduction according to both medium and apparatus protection levels

ABSTRACT

In a reproduction apparatus, for reproducing an original signal conveyed as main data by a data medium such as a recording disk or broadcasting system, with medium protection data which are specific to the data medium being conveyed together with the main data, the apparatus includes a section for generating apparatus protection data which are specific to the reproduction apparatus, a section for combining the apparatus protection data with the medium protection data to define a protection level, and a section for applying the protection level to restrict reproduction of the original signal, with stepwise variations in restriction occurring in accordance with changes in protection level. The medium protection data may include information for specifying restricted reproduction of portions of the original signal, such as by producing degraded resolution within specified regions of specified frames of a video signal.

This application is a continuation of application Ser. No. 09/469,499filed Dec. 22, 1999, which is a division of application Ser. No.08/391,861 filed Feb. 22, 1995, abandoned.

DESCRIPTION BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a data reproduction protection method,and a data reproduction apparatus for implementing such a protectionmethod, whereby reproduction of a signal represented by digital datasuch as a recorded digital video signal can be selectively restricted.

2. Description of the Prior Art

In the following, the term “data medium” is to be understood in a verygeneral sense, as applying for example to broadcasting systems whichtransmit data such as video and/or audio data, in which case thereceived data may be the object of reproduction protection, and asapplying also to any type of recording medium such as recording disks ortapes, etc., in which case playback data derived from the recordingmedium may be the object of reproduction protection. The reproductionprotection may serve to selectively restrict viewing, hearing or copyingof the data.

In the prior art, various types of reproduction protection method havebeen applied in fields such, as CATV (cable television) and satellitetelevision broadcasting. One method is to execute scrambling processingof transmitted video and audio data, and to insert a copyright code intothe data, for thereby dividing the, data into portions which can befreely reproduced and portions for which a fee must be paid in order toreproduce the data. When a program for which payment of a fee isnecessary is received by a receiving apparatus, the program can beunscrambled and reproduced only if specified payment conditions aresatisfied.

In the case of recorded media, one method of reproduction protectionwhich is applicable to the DAT (digital audio tape recorder) recordingsystem is the SCMS (serial copy management system). With that method,the playback DAT signal from a DAT playback apparatus has a main ID(identification) number which includes a copy inhibit code, whereby asingle [copy enable—copy inhibit] sequence is ensured, so that a usercan only make a single copy of a pre-recorded digital audio tape.

However with such prior art methods of reproduction protection there areonly two control possibilities, i.e. reproduction is made eitherpossible or impossible. It has not been possible hitherto to provide agradually varying degree of restriction of reproduction of a signalconveyed by a data medium. Thus, such a reproduction protection methodcan only be used for a single purpose, e.g. for management of paymentfees, or for copyright protection. Moreover with such a prior artreproduction protection method, since the data which are to be protectedexist only in a transmitting medium or recording medium prior to beingreproduced, it has not been possible to provide a varying degree oflimitation of reproduction capability in accordance with some conditionof the reproduction apparatus. Thus in some cases, the degree ofprotection may be excessively severe, or excessively lax, so that it isdifficult to achieve an effective degree of protection. For example,certain types of scenes recorded on a video tape may be permitted to beviewed in a certain country, such as the U.S.A., but may not bepermissible in other countries. It would thus be advantageous to ensurethat when that video tape is played on a reproduction apparatus which issold to the public in such other countries, reproduction protection isautomatically applied such that the aforementioned scenes will not bereproduced, or will not be clearly reproduced. However in the prior art,such a feature has not been possible.

SUMMARY OF THE INVENTION

It is an objective of the present invention to overcome the problems ofthe prior art set out above, by providing a reproduction protectionmethod and apparatus whereby information specifying a degree ofrestriction of reproduction of an original signal is conveyed (e.g. by arecording medium or signal transmission medium) together with dataexpressing the original signal, whereby information specifying a degreeof restriction of reproduction of the original signal are generated by areproduction apparatus which operates on the conveyed data, and wherebyinformation specifying a degree of restriction which is actually appliedto reproduction of the original signal is derived based on a combinationof the restriction information conveyed by the data medium and therestriction information generated by the reproduction apparatus.

More specifically, the invention provides a reproduction protectionmethod comprising: attaching medium protection data to main data whichare conveyed by a data medium, said main data representing an originalsignal;

supplying the main data and medium protection data, via the data medium,to a reproduction apparatus;

generating apparatus protection data by the reproduction apparatus;

determining a protection level by combining the medium protection dataand the apparatus protection data; and

controlling the reproduction apparatus to utilize the main data toreproduce the original signal in accordance with the protection level.

It is a further objective of the invention to overcome the aboveproblems by providing a reproduction apparatus providing reproductionprotection, for operating on main data representing an original signaland medium protection data expressing a medium protection level, saidmain data and medium protection being conveyed by a data medium, theapparatus comprising:

means for detecting said medium protection data to obtain a mediumprotection signal expressing said medium protection level;

means for generating an apparatus protection signal expressing anapparatus protection level which has been assigned to said reproductionapparatus;

means responsive to said medium protection signal and apparatusprotection signal for determining a final protection level in accordancewith a combination of said medium protection level and apparatusprotection level;

means for executing reproduction of said original signal by utilizingsaid main data, including means for selectively restricting saidreproduction in accordance with said final protection level.

With such a method and apparatus for reproduction protection, theprotection level can be determined in accordance with the mediumprotection data, and hence can be determined in accordance with thewishes of the manufacturer of the data medium, or of the copyright ownerof the main data. In addition, the protection level which is actuallyapplied (i.e. the final protection level) is also determined inaccordance with the apparatus protection data, which can be specified bythe manufacturer or the seller of the reproduction apparatus. As aresult, when the main data are to be reproduced (for example, duringplayback of a recording disk or tape), a graduated degree of limitationof reproduction is implemented, with that degree of limitation beingdetermined by the final protection level, i.e. being determined inaccordance with a combination of the requirements of the data mediummanufacturer or the copyright owner of the main data and therequirements of the manufacturer or seller of the reproductionapparatus. In that way, considerable flexibility can be ensured inselectively restricting reproduction of signals which are conveyed forexample by recording disks or tapes or by broadcasting systems.

In particular, the invention enables such reproduction restriction to beapplied to specific frames or sequences of frames of a video signal, orto specific regions within each of a sequence of frames.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general system block diagram of a first embodiment of theinvention, which is a CD player providing reproduction protection inaccordance with the present invention, for use in describing the basicprinciples of the invention;

FIG. 2 is a matrix diagram showing an example of how final protectionlevels are determined in a reproduction apparatus according to thepresent invention;

FIG. 3 shows specific examples of how medium protection levels can beassigned;

FIG. 4 shows specific examples of how apparatus protection levels can beassigned;

FIG. 5 is a general system block diagram of a second embodiment, whichis a specific configuration for the apparatus of FIG. 1, whereinprotection control is applied to a data decompression section;

FIG. 6 shows examples of relationships between final protection levelvalues and video picture visibility grades, for three different methodsof protection control of a video signal;

FIG. 7 is a general system block diagram of a third embodiment, which isa specific configuration for the apparatus of FIG. 1, wherein protectioncontrol is applied to a video reproduction control section;

FIG. 8 is a conceptual diagram for describing how time-axis protectionand spatial-domain protection control can be applied to a video signalwith the present invention;

FIG. 9 is a diagram for describing how video, audio and protection datacan be conveyed in a data stream in accordance with the MPEG1 standards;

FIG. 10 is a block diagram of an example of the internal configurationof a video reproduction control section in the embodiment of FIG. 7;

FIG. 11 is a general system block diagram of a fourth embodiment, whichis a specific configuration for the apparatus of FIG. 1, whereinprotection control is applied to a video reproduction control sectionand also to an audio reproduction control section;

FIG. 12 shows examples of relationships between final protection levelvalues and audio signal audibility grades, for three different methodsof protection control;

FIG. 13 is a block diagram of an example of the internal configurationof an audio reproduction control section in the embodiment of FIG. 11;

FIG. 14 is a matrix diagram for illustrating how variable ranges can bedefined for final protection level values, by a fifth embodiment of theinvention;

FIG. 15 is a general system block diagram of the fifth embodiment,wherein a final protection level can be modified by operation of aswitch provided on the reproduction apparatus; and

FIG. 16 shows relationships between medium protection level values andsettings of a modification switch in the embodiment of FIG. 15, for eachof respective values of the apparatus protection level.

DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the invention will now be described, in which the datamedium is assumed to be a recording medium, specifically a CD (compactdisk), having video and audio signal data recorded thereon. In thefollowing, such data representing original signals which are to bereproduced from the data medium will be referred to in general as themain data, to distinguish these from protection data, which are alsoconveyed by the data medium as described hereinafter. It will further beassumed that the original video and audio signals have been encoded byhigh-efficiency compression encoding using the MPEG1 algorithm, prior torecording. The MPEG1 algorithm is described for example in“International Standards for Multimedia Encoding”, edited by Yasuda,published by the Maruzen company in Japan. FIG. 1 is a diagram fordescribing the general features of the reproduction protection methodand reproduction protection apparatus.

Protection Information Provided on Recording Medium

The concept of medium protection data will first be described, referringto FIG. 1, in which data recorded on a CD (compact disk) 1 are read outfrom the disk to obtain an input signal for a demultiplexer 10 of a CDplayer 2, which is shown in block diagram form and which is configuredto provide reproduction protection control in accordance with thepresent invention. The CD 1 has video and audio signals recorded thereonas digital data (referred to in the following as the main data), usingMPEG1 compression encoding. Protection data, which are predetermined inaccordance with the contents of the main data and will be referred to asthe medium protection data, are also recorded on the CD 1. The mediumprotection data consist of information to be used in selectivelyrestricting reproduction of the main data, as described hereinafter. Themedium protection data can for example be recorded within the main codeand sub-code header regions of the CD 1, or in the user region of thecompressed data. The medium protection data expresses a protectionlevel, referred to as the medium protection level, which can for exampletake values which successively increase in five steps, from 1 to 5, asshown in FIG. 2 and described hereinafter. In that case, the mediumprotection data can express the medium protection level by 3 bits. Ifseparate medium protection levels are provided for the recorded videoand audio data, then these can be expressed by two sets of 3 bits. Thehigher the number of the medium protection level, the greater is thedegree of protection (i.e. the greater becomes the degree of restrictionof reproduction of the recorded video or audio signal). The limitationof reproduction can for example by effected, in the case of video data,by operating on the playback data obtained from the CD 1 such as toproduce an output video signal, from the apparatus of FIG. 1 which willresult in a mosaic pattern being produced within all or a specificregion of a resultant displayed picture, as described hereinafter.

The medium protection level which is expressed by the medium protectiondata is predetermined in accordance with the wishes of the manufactureror seller of the data medium (CD 1), or of the owner of the copyrightfor the main data. FIG. 3 shows two examples of medium protection data,each expressing 5 values of medium protection level. In the firstexample, limitation of reproduction is based upon the filmclassification system (i.e. movie ratings system) which is used in theU.S.A. In the case of a film which is rated “free”, no restriction onreproduction is imposed by the medium protection data. If the movie israted “PG” (i.e. parental guidance), then a moderate degree ofrestriction (protection level 1) is applied, and so on with increasingdegrees of restriction for the “R” and “X” ratings. In the secondexample, limitation of reproduction is based on the rights of thecopyright owner, providing successively increasing degrees ofrestriction of reproduction as the protection level increases from 1 to5.

The medium protection data is a combination of data for expressing atleast one medium protection level as described above, and protectionposition information which specifies the position (within the encodedmain data) at which the protection is to be applied. It is an essentialfeature of the present invention that the medium protection data canassign the medium protection level in units of frames of the videosignal. That is to say, limitation of reproduction of individual framescan be controlled. In addition, limitation of reproduction of one ormore specific regions within a specific frame (or sequence of specificframes) can also be predetermined by the medium protection data. In thatcase, for example, a region formed of a number of fixed-size blocks ofpixels can be converted to a blank region, or filled with a mosaicpattern, in the final display picture that is obtained from the outputvideo signal from the apparatus of FIG. 1. That is to say, theprotection position information can be used to specify not only aspecific frame, but also to specify one or more specific regions withina frame.

Alternatively, the protection position information can specify anidentical medium protection level for the entirety of each of asuccession of video signal frames, or specify an identical mediumprotection level for one or more specific regions within each of asuccession of frames.

The term “protection position information” is used here, since it maynot be necessary to record explicit data constituting the protectionposition information on the CD 1. Instead, that information can beinherently constituted by the positions at which respective mediumprotection data are located within the stream of compressed encoded maindata that have been recorded on the CD 1. For example, the apparatus maybe configured such that if the encoded data for a video signal frame areimmediately preceded by a portion of medium protection data, then thatindicates that the medium protection data portion is to be applied tothat frame. If the medium protection data portion is to be applied toone or more regions within that frame, rather than the entire frame,then the medium protection data portion which immediately precedes thecompressed encoded frame in the recorded data can include at least twovalues for each of these regions, for specifying the respectivepositions of the regions. In that case, explicit protection positioninformation must be recorded as data on the CD 1, as part of the mediumprotection data.

Protection Information Generated by Reproduction Apparatus

With the method and apparatus of the present invention, a reproductionapparatus can be configured to produce predetermined protection datawhich are specific to that reproduction apparatus. For example, the CD 1in FIG. 1 is played by a reproduction apparatus 2 which is provided witha presettable memory device which will be assumed to be a ROM (read-onlymemory) which generates apparatus protection data expressing aprotection level referred to in the following as an apparatus protectionlevel. The apparatus protection level is specified beforehand by themanufacturer or the seller of the reproduction apparatus. In the sameway as for the medium protection data described above, the apparatusprotection level can take a plurality of values, corresponding torespectively different degrees of limitation of reproduction of maindata which are obtained from a data medium. It will be assumed that thenumber of apparatus protection level values is 4, i.e. from 1 to 4, sothat the apparatus protection data can consist of two bits. The higherthe apparatus protection level number, the greater becomes the degree ofprotection, i.e. the greater becomes the degree of reproductionlimitation.

The contents of the apparatus protection data ROM cannot be rewritten bythe user. In the embodiment of FIG. 1, each time that power to theapparatus is switched on, the apparatus protection data are read outfrom the ROM, and thereafter reproduction is executed in accordance witha combination of the apparatus protection level specified by theapparatus protection data and the medium protection level which isspecified by the medium protection data.

FIG. 4 shows three examples of how the apparatus protection level can beassigned. In the first example, the apparatus protection level is presetin accordance with the country in which the reproduction apparatus is tobe used. If the reproduction apparatus is to be used in the U.S.A. forexample, then it is possible that the apparatus protection level couldbe set to a low value such as 1. In the case of a reproduction apparatuswhich is to be used in other parts of the world, such as Europe, Japanand Taiwan, which have varying degrees of restrictions on videosoftware, the apparatus protection level could be set to higher values,as illustrated. In that way, video scenes which are not permissible inone country can be automatically eliminated (partially or completely),e.g. by insertion of mosaic pattern regions in the resultant displaypicture, by using the apparatus protection level and medium protectionlevel in combination as described hereinafter.

With the second example in FIG. 4, the apparatus protection level ispredetermined in accordance with the type of person who is expected touse the reproduction apparatus. If the reproduction apparatus is to beused only by adults, for example, then the apparatus protection levelcan be set at a low value such as 1. If the reproduction apparatus willbe used by children, the apparatus protection level can be set to a highvalue such as 4. In that way, video scenes or audio content which areconsidered unsuitable for children can be partially or completelyrestricted from being reproduced.

With the third example in FIG. 4, the protection level that is set bythe apparatus protection data is predetermined in accordance with theapplications for which the reproduction apparatus will be used. Forexample if the reproduction apparatus is to be sold to the public, thenthe apparatus protection level can be set to a value such as 1 or 2,whereas if the reproduction apparatus is intended to be used fordemonstration purposes in a shop, then the apparatus protection levelcan be set to a different value, i.e. 3 or 4, and the apparatus of FIG.1 controlled such that only certain scenes which should be of interestto possible customers of the shop will be displayed. In that way, theapparatus protection level can be set in accordance with the applicationobjectives of the reproduction apparatus.

The overall features of reproduction protection will now be described,referring to FIG. 1. Firstly, data recorded on the CD 1 are read out, asan input signal to the demultiplexer 10. The recorded data on the CD 1consist of the compressed encoded main data (i.e. compressed encodedvideo and audio data) which are multiplexed with the medium protectiondata. The demultiplexer 10 separates the compressed encoded main datafrom the medium protection data, and supplies the medium protection datato a medium protection signal detection section 11 while supplying thecompressed encoded main data to a video decoder section 15. As describedhereinabove, the medium protection data may inherently specifyprotection position information, or may include explicit protectionposition information. The medium protection signal detection section 11serves to detect the protection position information, and generates acorresponding protection position signal, which indicates those portionsof the main data to which the medium protection data applies (e.g.specific video signal frames, and/or block regions within specificframes). The protection position signal. is supplied to a protectioncontrol signal generating section 14. The medium protection signaldetection section 11 is further responsive to the medium protection datafor generating a corresponding medium protection signal, which expressesthe medium protection. level and is supplied to a final protection leveldetermining section 13.

The final protection level determining section 13 basically consists ofa matrix ROM in this embodiment, i.e. a ROM which stores a pattern ofrelationships between respective combinations of medium protectionlevels and apparatus protection levels and resultant final protectionlevels. The operation of the matrix ROM will be described referring tothe matrix diagram of FIG. 2, which shows an example of how the contentsof that ROM are read out in response to combinations of mediumprotection level and apparatus protection level values. There are fivepossible values (designated as A to E respectively) for the finalprotection level, successively increasing in degree of reproductionlimitation in the sequence A, B, C, D, E. FIG. 2 shows an example ofvarious values of the final protection level which are determined byrespective combinations of values of the medium protection level andapparatus protection level, i.e. the values in the range A to E whichare located at respective intersections between rows and columns of thematrix in FIG. 2. Thus for example if the medium protection level is 4and the apparatus protection level is 2, then the final protection levelwill be B.

It is necessary to clearly distinguish between the ROM of the apparatusprotection signal generating section 12 and the matrix ROM of the finalprotection level determining section 13. The contents of the ROM of theapparatus protection signal generating section 12 can be set inaccordance with the requirements for a particular reproductionapparatus, whereas the contents of the matrix ROM of the finalprotection level determining section 13 will in general be common to alarge number of reproduction apparatus units.

The final protection level determining section 13 generates an outputsignal, referred to as the final protection level signal, whichexpresses the final protection level that has been determined, andsupplies that signal to the protection control signal generating section14. In response to that signal, and the protection position signal, theprotection control signal generating section 14 generates a signalreferred to as the protection control signal, which is supplied tocontrol a section which will be referred to as the video decoder section15. For simplicity of description, only video signal reproduction willbe considered at this stage, and the video decoder section 15 should beunderstood as a section which converts the compressed encoded video data(main data) from the demultiplexer 10 to a standard (analog) videosignal. As the stream of compressed encoded main data flows into thevideo decoder section 15 from the demultiplexer 10, the protectioncontrol signal controls the video decoder section 15 such as to applyreproduction protection in accordance with the final protection levelvalues, at the respective positions within that data flow which arespecified by the protection position information. The video decodersection 15 thereby produces an output video signal which will result invideo pictures in which reproduction of the main (video) data is limitedin accordance with the final protection level values. As will beunderstood from the above, the final protection level values may changefrom frame to frame of the video signal, in accordance with changes inthe medium protection level.

A first example of limitation of reproduction in accordance with thefinal protection level will be described, which is implemented bycontrolling the expansion and decoding of the main data by the videodecoder section 15. The example will be described referring to theembodiment of FIG. 5, in which the reproduction apparatus is again a CDplayback apparatus, designated by numeral 3. Only the operation withregard to the video data of the main data from the CD 1 will bedescribed. In FIG. 5, a specific configuration for the video decodersection 15 of FIG. 1 is shown, made up of a variable-length decodingsection 15 a, a dequantizer section 15 b, an inverse transform section15 c and a video reproduction control section 15 d, with the compressedencoded video data being supplied from the demultiplexer 10 to thevariable-length decoding section 15 a and with the final output (analog)video signal being produced from the video reproduction control section15 d. In this embodiment, the video data have been recorded on the CD 1after being subjected to compression by discrete cosine transformprocessing, and reproduction limitation is controlled by controlling theaccuracy of inverse DCT (discrete cosine transform) processing which iseffected by the inverse transform section 15 c. The protection controlsignal which is produced from a protection control signal generatingsection 14 a and supplied to control the inverse transform section 15 cis derived based on the medium protection data and apparatus protectiondata, in combination, as described above for section 14 in FIG. 1, i.e.the protection control signal applies control in accordance with thefinal protection level.

The demultiplexed compressed encoded video data read from the CD 1 aresubjected to variable-length decoding in the variable-length decodingsection 15 a, and then to dequantization in the dequantizer section 15b. The resultant compressed data are then subjected to inverse DCTprocessing in the inverse transform section 15 c, with the transformprocessing being selectively modified in accordance with the protectioncontrol signal. The resultant decompressed data are then processed inthe video reproduction control section 15 d to obtain the final outputvideo signal. The effect of reproduction limitation controlled by theprotection control signal acting on the inverse transform section 15 cis to selectively produce a degree of blurring or formation of a mosaicpattern within the pictures which are displayed using the final outputvideo signal. Such a degree of blurring will be referred to as thevisibility grade. An example of the relationship between the visibilitygrade and the final protection level values A to E (which are determinedby the protection control signal generating section 14 a as describedhereinabove, and are expressed by the protection control signal) isshown in the leftmost column of FIG. 6. If the protection level is A,i.e. minimum limitation of reproduction of the video data, then theprotection control signal is set to a state whereby it does not affectthe operation of the inverse transform section 15 c. If the protectionlevel is B, then the protection control signal controls the inversetransform section 15 c such as to operate on a block size of 8×8 pictureelements (i.e. the same block size which was utilized in the originalDCT processing), using the DC component value for each block, but usingonly two of the AC transform coefficients, with the values of all of theother transform coefficients being forcibly set to zero. This willresult in a substantial lowering of resolution of a display picture thatis produced based on the output video signal. If the protection level isC, then the protection control signal controls the inverse transformsection 15 c such as to operate on a block size of 8×8 picture elementsof a video signal frame, using only the DC component for each block,(i.e. the DC component is the only transform coefficient used). In thiscase, since all of the picture elements within an 8×8 picture elementblock will have identical video signal values, this will result in amosaic pattern being formed in the finally obtained picture. If theprotection level is D, then the protection control signal controls theinverse transform section 15 c such as to operate on a block size of16×16 picture elements, using only the DC component values. This willagain result in a mosaic pattern being formed, in which the blocks ofthe pattern are of larger size then for the case of protection level C,i.e. a mosaic pattern of macroblocks is formed, thereby furtherdegrading the degree of visibility of the resultant picture. If theprotection level is E, then the video data obtained from the inversetransform section 15 c are replaced by different video data (producedfrom a source not shown in the drawing), which are produced from thevideo reproduction control section 15 d as the final video signal, andwhich will produce a predetermined picture or pictures. Such apredetermined picture might for example display a warning messageconcerning copyright protection.

With the MPEG1 algorithm, a block size of 8×8 picture elements is usedin the DCT processing. The transformed block is expressed by a DCcomponent (i.e. DC coefficient) and a plurality of coefficients (the ACcoefficients) which represent signal level values at respectivelydifferent successively increasing frequencies. Thus if for example theinverse transform section 15 c is controlled such that only the DCcoefficient and the two lowest-frequency AC coefficients are used, inthe inverse DCT operation for each block, then a specific reduction inresolution of all (or a specific part) of the resultant display picturecan be achieved in a very simple manner.

Similarly if only the DC component for a block is used in the inverseDCT processing, with all of the AC coefficients set to zero, then all ofthe signal level values for the picture elements of a block will be setto an identical value, in the resultant video signal obtained from theinverse DCT operation. Hence, a mosaic pattern can very easily be formedin the resultant picture that is obtained using the final output videosignal. Moreover if, for each of respective 16×16 element macroblocks(i.e. each consisting of four 8×8 picture element blocks), only the DCcoefficient for a specific one of the 8×8 element blocks is used (forexample, the DC coefficient for the upper leftmost one of the 8×8element blocks) in the inverse DCT processing for all of the four 8×8element blocks constituting the 16×16 element macroblock, with all ofthe AC coefficients set to zero, then a mosaic pattern will be formedwhich is substantially coarser than the mosaic pattern which is formedby using the 8×8 element blocks.

It can thus be understood that with the above embodiment of theinvention, applied to video data which have been subjected tohigh-efficiency compression encoding using a data transform operation,stepwise changes in a degree of restriction of reproduction of the videodata can be easily accomplished by effecting stepwise changes in adegree of resolution of a finally obtained picture, or in a portion ofthat picture, and that such stepwise changes in resolution can be easilycontrolled in accordance with the final protection level which has beenestablished based on the medium protection data and apparatus protectiondata. In particular, when such control is applied to the inverse DCTprocessing, it is possible to easily effect stepwise changes in thevisibility grade, i.e. in the picture resolution, through use of unitblocks of picture element values which are basic to the transformprocessing. Such a type of control of the visibility grade, operatingwithin each frame of the video signal, can be considered as applyingprotection in a (2-dimensional) spatial domain.

With a video data encoding method such as the DCT method, the outputdigital signal that is produced from the inverse DCT circuit consists ofsequential sets of data, each consisting of successive picture elementvalues for the respective picture elements of a unit block (e.g. a blockof 8×8 picture elements) of a video signal frame. In order to convertsuch a digital signal into a normal digital video signal, it isnecessary to first temporarily store the data produced from the inverseDCT circuit in a video memory (e.g. a frame memory), then to read outthe video data in the correct sequence (i.e. as successive pictureelement values in successive picture scanning line intervals). Thatoperation is the basic function of the video reproduction controlsection 15 d in FIG. 5. FIG. 7 shows another embodiment of theinvention, in which control for reproduction protection is applied tothe video data which have been produced from the inverse transformsection 15 c, i.e. in which control by the protection control signal inaccordance with the final protection level is applied to a videoreproduction control section which is configured such as to respondappropriately to the protection control signal, and is designated as 15d′. Apart from this feature, the configuration and operation of thisembodiment is identical to that of FIG. 5 described above. The videoreproduction control section 15 d′ includes a frame memory, into whichoutput data from the inverse transform section 15 c are temporarilywritten, and then read out in the appropriate sequence as describedabove, to obtain the final output video signal.

In this embodiment, the degree of reproduction limitation is controlledby “thinning out” frames of the video data that are used to form thefinal output video signal, with the degree of “thinning out” beingdetermined by the final protection level. That is illustrated by thecentral column in FIG. 6, in which such a type of control is referred toas time domain protection. In the example of FIG. 6, when the finalprotection level is A, then all of the frames of video data which aresuccessively written into the frame memory of the video reproductioncontrol section 15 d′ are used to form the final output video signal. Ifthe final protection level is B, then the protection control signal fromthe protection control signal generating section 14 b controls the videoreproduction control section 15 d′ such that only one out of every 15frames of video data supplied from the inverse transform section 15 c isused to form the final output video signal. Specifically, one out ofevery. fifteen frames of video data from the inverse transform section15 c is held stored in the frame memory of the video reproductioncontrol section 15 d′ for fifteen successive frame periods, and isrepetitively read out during that time, to form the final output videosignal. Thus a type sample-and-hold operation is performed using theframe memory in the video reproduction control section 15 d′, wherebythe finally obtained picture will change once in every 0.5 seconds. Ifthe final protection level is C, then the video reproduction controlsection 15 d′ is controlled such that the contents of the frame memoryare updated only once in every 60 frame periods, i.e. the finallyobtained picture will change only once in every 2 seconds. If the finalprotection level is D, then only the video data of certain specificframes (or one specific frame) are written into the frame memory of thevideo reproduction control section 15 d′ and read out to obtain thefinal output video signal. In that way, for example, only a portion ofthe video data (e.g. a portion which is not subject to copyrightprotection) will be displayed. If the protection level is E, then thevideo data for a predetermined picture are written into the frame memoryof the video reproduction control section 15 d′ and repetitively readout to display only that predetermined picture, which can be for examplea warning message concerning copyright protection.

Alternatively, control of the degree of reproduction limitation can beperformed by arranging that the protection control signal from theprotection control signal generating section 14 b acts on the videoreproduction control section 15 d′ such as to vary (in accordance withthe final protection level) the number of gradations provided by eachvideo data sample, i.e. to vary the number of amplitude levels that canbe expressed by each sample. That can be performed by setting one ormore low-order bits of each data sample to a fixed value, e.g. 0. Forexample if the LSB is always set to 0, then the number of possiblegradations is reduced by half, and a corresponding lowering ofresolution of the finally obtained display picture is achieved. The bitsin each digital data sample which are not fixed in that way Will bereferred to in the following as the effective bits of the sample. Suchgradation control based on the numbers of effective data bits isillustrated by the right-side column in FIG. 6. In that example, if thefinal protection level is A, then the protection control signal from theprotection control signal generating section 14 b has no effect on theoperation of the video reproduction control section 15 d′, so that eachvideo data sample used to form the output video signal has the standardnumber of effective bits, i.e. 8 bits. If the final protection level isB, then the protection control signal controls the video reproductioncontrol section 15 d′ such that the number of effective bits/sample ofthe output video signal is reduced to 4 (i.e. by rounding-off thelow-order 4 bits to zero). If the final protection level is C, then theprotection control signal controls the video reproduction controlsection 15 d′ such that the number of effective bits/sample is 2 (i.e.all except the two high-order bits are set to zero), so that the pictureresolution is further degraded. Similarly, if the final protection levelis D, then the video reproduction control section 15 d′ is controlledsuch that the number of effective bits is reduced to 1. If theprotection level is E, then the video data for a predetermined pictureare written into the frame memory of the video reproduction controlsection 15 d′ and repetitively read out as the final output videosignal, to display only that predetermined picture.

It would be equally possible, as indicated by the broken-line connectionfrom the protection control signal generating section 14 b to thedequantizer section 15 b in FIG. 7, to arrange that the protectioncontrol signal from the protection control signal generating section 14b acts on the dequantizer section 15 b such as to vary (in accordancewith the final protection level) the number of effective bits of eachoutput datum from the dequantizer section 15 b. That will provide asimilar effect to that described above for the case in which control iseffected through the video reproduction control section 15 d′.

Another method which may be used to control the degree of reproductionlimitation is to apply the protection control signal from the protectioncontrol signal generating section 14 b such as to control thevariable-length decoding section 15 a. In that case, the protectioncontrol signal is arranged to act on the variable-length decodingsection 15 a such that, as the protection level is increased from A toE, data having a long code length are set to zero, i.e. are ignored.This will result in a lowering of resolution in the final picture thatis obtained from the output video signal.

It should be noted that reproduction limitation control can be executedby a combination of control acting along the time axis and controlacting in a spatial domain (i.e. within individual frames). That pointis illustrated conceptually in FIG. 8, in which successive verticallines 20 represent sequential frames of the video signal that isrecorded on the CD 1. (For simplicity of description, it will be assumedthat the final protection level is identical to the medium protectionlevel). Together with each video signal frame data portion on the CD 1,a medium protection data portion is recorded, which may include positioninformation specifying a region within the frame within which displayresolution is to be lowered, to a degree that is in accordance with thefinal protection level. In this example there are two possible basicdisplay conditions for each frame, i.e. non-display or display (with oneor more degraded resolution regions possibly being formed). To achievethis, the medium. protection data assigned to each frame includes a1-bit flag, whose 1 or 0 logic state designates either display ornon-display for the frame. If that flag bit indicates that none of theframe is to be displayed, the condition is indicated by a “x” symbol inFIG. 8, while if the flag bit indicates that the frame is to becompletely or partially displayed, that condition is indicated by a “o”symbol in FIG. 8. In the example of FIG. 8, a “o” condition is specifiedfor each of the ten consecutive frames designated as F_(A), indicatingthat each frame is to be displayed. In addition, the medium protectiondata of each of these frames includes position information for adegraded resolution region. The resultant display picture is designatedby numeral 21, containing a degraded resolution region 22, which isrectangular and is, shown as a hatched-line region. The degraded.resolution region 22 is formed by a plurality of 16×16 elementmacroblocks, and for each of the frames F_(A), the correspondingposition information in the medium protection data specifies twoaddresses of macroblocks (designated as 22 a and 22 b, located at theupper left-side and lower right-side corners of the mosaic region 22)within the frame, to thereby specify the position and size of arectangular region which is the degraded resolution region 22.

Similarly, a set of four successive frames F_(B) is each to bedisplayed, but with a degraded resolution region formed in the finaldisplay picture, as indicated by numeral 24. In this case the degradedresolution region is formed of two adjoining rectangular regions, sothat it is necessary for the position information in the mediumprotection data to specify the positions of two pairs of macroblockswithin the frame, i.e. the pair of addresses of macroblocks 24 a, 24 band the pair of addresses of macroblocks 24 c, 24 d in FIG. 8.

It can thus be understood that in this case, reproduction protection isapplied by a combination of control with respect to the time axis, andcontrol with respect to (2-dimensional) space within each frame. It canbe further understood that the invention enables extremely precisecontrol of reproduction limitation, which is determined in accordancewith the final protection level.

With data transmission in accordance with the MPEG1 system (i.e. basedon the ISO-11172-3 standards), data are transmitted as successive packsof data, which are time-division multiplexed, as illustrated by the dataflow 40 shown in FIG. 9. Each pack is made up of a leading portion suchas the portion 41, which contains information including a pack startcode and a stream identifier which distinguishes the data conveyed bythat pack from that of other packs (e.g. to distinguish between video,audio or other data), and a main data portion such as portion 42. Inthis example each main portion consists of either compressed encodedvideo data such as portion 42, encoded audio data such as portion 43, orprotection data such as portion 44. In this example it will assumed thatprotection of the form shown in FIG. 8 is applied to the video data, soan individual protection data portion may be assigned to each of aplurality of video signal frames, i.e. video data frames can. beconveyed. by respective packs, each preceded by a protection data pack.In that case, each protection data pack in the example of FIG. 9consists of a 3-bit portion which specifies the medium protection level,a 1-bit frame flag specifying whether or not the frame is to bedisplayed (as described above for FIG. 8), a portion which specifies thenumber of macroblock start/end address pairs (to be utilized when atleast one degraded resolution region is to be formed within the frame,e.g. as for each of the frames F_(A) and F_(B) in FIG. 8), followed bythe pairs of macroblock start/end addresses (e.g. the pair of addressesof macroblocks 24 a, 24 b, then the pair of addresses of macroblocks 24c, 24 d, for each of the frames F_(B) in the example of FIG. 8).

FIG. 10 shows a specific internal configuration for the videoreproduction control section 15 d′ of the embodiment of FIG. 7. In FIG.10, the output data from the inverse transform section 15 c are suppliedvia a line 50 to a gradation control section 51, which is controlled byone of two protection control signals that are generated from theprotection control signal generating section 14 b, and resultant outputdata from the gradation control section 51 are transferred through aswitch 52, which is controlled by the other one of the protectioncontrol signals. Data transferred through the switch 52 are written intoa frame memory 53, and are subsequently read out from the frame memory53 in the appropriate sequence to constitute successive frames of theoriginal video signal. The digital video signal thereby produced fromthe frame memory 53 is supplied to a digital/analog converter 54, toobtain an analog video signal as the final output signal. So long as theswitch 52 is held closed, the contents of the frame memory 53 will becompletely updated once in each frame period of the video signal, sothat data of a new frame will be sequentially read out from the framememory 53. However if the switch 52 is held closed during an integralnumber of frame intervals, then the most recently stored contents of theframe memory 53 will be repetitively read out during each of these frameintervals, i.e. the last frame will be continuously outputted. It willthus be apparent that this circuit can implement the time-axisprotection operation described above on successive frames, if the switch52 is controlled in accordance with the status of the frame bit that iscontained in the medium protection data.

The gradation control section 51 operates on each digital video signalsample (in general, each 8-bit datum) that is supplied from the inversetransform section 15 c, to set the low-order bits of each sample inaccordance with the final protection level. For example referring to theright-side column in FIG. 6, if the final protection level is B, thenthe gradation control section 51 sets all of the four low-order bits ofeach sample to a predetermined value, e.g. 0. If the protection level isD, then all of the seven low-order bits of each sample are set to 0.

If reproduction restriction is to be applied within a video signalframe, then the protection control signal generating section 14 bresponds to the protection position signal such as to apply theabove-mentioned protection control signal to the gradation controlsection 51 during one or more specific time intervals within thecorresponding frame interval, with each of these specific time intervalsbeing determined based on one of the macroblock start/end address pairswhich are shown in FIG. 9, described above. In that way, reproductionlimitation can be applied within specific regions of a frame, asillustrated in FIG. 8, i.e. the spatial-domain protection operationdescribed above can be applied.

It will be understood that in practical terms, each “start address” willdefine a time-axis position, within a frame period, of the data samplecorresponding to an uppermost left-side pixel of a rectangular regionwithin the frame, while the “end address” similarly defines the positionof a data sample corresponding to a lowermost right-side pixel of thatregion. Such time relationships can be readily established by well-knowntechniques for operating on a digital video signal, so that detaileddescription is omitted.

In the above embodiments, only reproduction protection of video data hasbeen described. FIG. 11 shows another embodiment of the invention, inwhich reproduction protection of both audio and video data is applied.Only the points of difference between this embodiment and previousembodiments will be described. A CD reproduction apparatus 5 of thisembodiment differs from that of FIG. 7 by including circuits fordecoding and dequantizing an encoded digital audio signal that has beenrecorded on the CD 1, by an audio decoding section made up of avariable-length decoding section 16 a, a dequantizer section 16 b, asub-band combining section 16 c and an audio reproduction controlsection 16 d. The compressed encoded audio data are separated from thevideo and protection data contained in the input data stream, by thedemultiplexer 10, and are supplied as input data to the variable-lengthdecoding section 16 a, with an output audio signal being produced fromthe audio reproduction control section 16 d. This embodiment furtherdiffers from that of FIG. 7 in that the protection control signalgenerating section 14 c of this embodiment produces not only a firstprotection control signal which acts on either the video reproductioncontrol section 15 d′ or dequantizer section 15 b to apply video signalreproduction protection by varying the number of bits per datum, asdescribed hereinabove for the protection control signal of theembodiment of FIG. 7, but also a second protection control signal whichacts on the audio reproduction control section 16 d or dequantizersection 16 b to apply audio signal reproduction protection, as describedin the following. For simplicity of description, it will be assumed thatthe second protection control signal is produced in accordance with thefinal protection level that is derived for reproduction protection ofthe the video data, as described hereinabove. However in general,separate medium protection levels and separate apparatus protectionlevels would be specified for the video and audio data, i.e. to obtainseparate final protection levels for video and audio data.

FIG. 12 is a table illustrating three possible methods of applying audiosignal reproduction protection with the embodiment of FIG. 11. With eachof the three examples shown in FIG. 12, five different audibility gradescan be selected for the output audio signal produced from the audioreproduction control section 16 d, in accordance with the finalprotection level, to effect audio signal reproduction protection.Firstly, the method illustrated by the leftmost column in FIG. 12 willbe described. In this case, audio signal reproduction protection isapplied by selectively restricting the bandwidth of the output audiosignal produced from the audio reproduction control section 16 d inaccordance with the final protection level. If MPEG1 audio signalcompression is used, then assuming a sampling frequency of 48 KHz, abandwidth of 24 KHz is available for the output audio signal. In thisexample, if the final protection level is A, then no bandwidthrestriction is applied, i.e. the audio bandwidth is 24 KHz. If the finalprotection level is B, then the audio signal bandwidth is restricted to18 KHz, if the protection level is C the bandwidth is restricted to 12KHz, if the protection level is D the bandwidth is restricted to 6 KHz,and if the protection level is E then no audio output signal isproduced.

Since MPEG1 audio compression utilizes sub-band encoding with 32 bands,such bandwidth restrictions can be effected by causing the secondprotection control signal to act on the dequantizer section 16 b such asto set the inverse quantization values corresponding to certainhigh-frequency bands to zero. Thus, audio reproduction protection bybandwidth control can be easily implemented.

A second method of audio signal reproduction protection will bedescribed referring to the central column in FIG. 12. In this case,time-axis protection is applied, by “thinning-out” of audio signalsample values that are supplied from the sub-band combining section 16 cand used in the audio reproduction control section 16 d to obtain theoutput audio signal. In this example, if the final protection level isA, then all of the audio sample values are used in deriving the outputaudio signal. If the final protection level is B, then one in every twosamples is held for two consecutive sample periods, by a sample-and-holdcircuit, i.e. only half of the total samples are used in deriving theoutput audio signal. If the protection level is C, then only one inevery three samples is used in deriving the output audio signal, i.e.one in every three successive samples is held for three consecutivesample periods. If the protection level is D, then only samples whichoccur during a specified interval are used in producing the output audiosignal. For example, this operation could be performed when only aspecified part of the recorded audio signal is to be allowed (by thecopyright owner) to be reproduced. If the final protection level is E,then no audio output signal is produced.

A third method of audio signal reproduction protection will be describedreferring to the rightmost column in FIG. 12. In this case, protectioncontrol is executed by effecting control of the number of gradationlevels provided by the audio data samples, in a similar manner to thatdescribed hereinabove for the video data. Generally, a digital audiosignal has 16 bits/sample. When the final protection level is A, thenall of these 16 bits are utilized, i.e. there is no limitation ofaudibility. If the final protection level is B, then the number ofeffective bits/sample is reduced to 12 (i.e. the low-order 4 bits ofeach 16-bit sample are fixed at 0), causing a lowering of quality of thereproduced audio signal. If the protection level is C, the number ofeffective bits is further reduced to 8, if the final protection level isD then the number of effective bits/sample is reduced to 4, and if thefinal protection level is E, then no audio output signal is produced.

It can thus be understood that the invention enables precise limitationof reproduction of a recorded audio signal together with limitation ofreproduction of the recorded video signal, in accordance with acombination of medium protection data and apparatus protection data.

FIG. 13 shows an example of the internal configuration of the audioreproduction control section 16 d of this embodiment. For the purpose ofdescription, it is assumed that each of the above-mentioned threemethods of protection control of the audio reproduction control section16 d is utilized, although in practice only one of these could beutilized. The circuit consists of a digital low-pass filter 61 whichreceives the output data samples from the sub-band combining section 16c via an input line 60, a sample-and-hold circuit 62 which can becontrolled to hold and output each data sample for a specific interval,a gradation control section 63 which effects the aforementioned controlof low-order bits of each audio data sample, to thereby control thegradation levels which can be expressed by each sample, a memory 64 fortemporarily holding successive data samples, and a digital-to-analogconverter 65 for converting the digital audio data to an analog audiosignal. The gradation control section 63 is controlled by a protectioncontrol signal to provide varying degrees of gradation in accordancewith the final protection level that has been determined for the audiodata, by setting varying numbers of low-order bits of each 16-bit audiodata sample to a fixed value as described above.

As shown, the protection control signal can also be applied to controlthe sample-and-hold circuit 62, to effect the above-described method ofreproduction protection control utilizing sample-and-hold processing ofthe audio data samples. Similarly, the protection control signal can beapplied to control the LPF 61, to achieve reproduction protectioncontrol by varying the bandwidth of the audio signal. It will be clearthat a simpler circuit configuration can be utilized that that shown inFIG. 13, if only one of the above three methods of protection control isapplied.

In each of the embodiments described above, there is a fixedrelationship pattern between combinations of the protection levels whichcan be expressed by the medium protection data and the protection levelswhich can be expressed by the apparatus protection data, and therespective final protection levels which are thereby obtained, i.e. therelationship pattern which is stored in the matrix ROM of the finalprotection level determining section 13, an example of which is shown inFIG. 2. However in some cases there may be a requirement for enablingsuch a relationship pattern to be selected from a number of differentrelationship patterns, which have varying degrees of protectionseverity. Specifically, it may be advantageous to provide thereproduction apparatus with a switch which can be operated by the personwho is in charge of the reproduction apparatus, such that the switch canbe used to select from a plurality of different relationship patterns,so that the degree of reproduction protection can be flexibly determinedby that person. In that way, the person in charge of the reproductionapparatus can ensure that the reproduction protection will beappropriate for the viewing audience. For example, an adult can set theswitch such as to ensure that unsuitable scenes cannot be viewed by anychildren who may use the reproduction apparatus. In that case, assumingfor example that the relationship pattern which is the least severe isthat shown in FIG. 2, the entire range of possible relationship patternsis illustrated in the table of FIG. 14. Here, for each combination ofprotection levels obtained from the medium protection data and apparatusprotection data, there is a corresponding range of one or more possiblevalues of final protection level, with that range extending from a leastsevere value to the most severe value (i.e. protection level E). Onemethod of implementing such a capability would be to provide a pluralityof matrix ROMs (or to define a plurality of separate matrix regions in aROM), for storing the respectively different relationship patterns.However an embodiment of the invention will now be described wherebysuch a capability can be easily implemented by a simple modification ofany of the embodiments of the invention that have been previouslydescribed.

The embodiment, which is a modification of the embodiment of FIG. 5, isshown in FIG. 15. The embodiment differs from that of FIG. 5 in beingprovided with a severity modification circuit 30 and a severitymodification setting switch 31. The severity modification circuit 30 isconnected between the final protection level determining section 13 andthe protection control signal generating section 14 a, and functions toselectively modify each protection level value which is read out fromthe matrix ROM of the final protection level determining section 13 (asdescribed hereinabove for the embodiment of FIG. 5), and to supply aresultant modified final protection level to the protection controlsignal generating section 14 a. The severity modification setting switch31 can be adjusted by the person who is in charge of the CD player, toselect one of five possible switch conditions which will be designatedas P_(A) to P_(E), respectively. The severity modification settingswitch 31 is coupled to control the severity modification circuit 30such that the severity modification circuit 30 executes protection levelmodification in accordance with the specific position at which theswitch is set, as described in the following.

The relationships between the five possible values of the mediumprotection level (determined by the medium protection signal detectionsection 11 as described hereinabove) and the five positions P_(A) toP_(E) of the severity modification setting switch 31, are shown for eachof the four possible values of the apparatus protection level(determined by the apparatus protection signal generating section 12),in diagrams (A) to (D) in FIG. 16. Referring first to diagram (A), ifthe switch position is P_(A), then the relationship between the mediumprotection level values, the apparatus protection level values and thefinal protection level values is left unchanged from those of thecorresponding column in FIG. 2, i.e. this setting of the severitymodification setting switch 31 provides the least severe degree ofreproduction protection. If the switch position is set to P_(B), thenthe least severe value which can be taken by the modified finalprotection level becomes level B. That is to say, if a protection levelA is established by the final protection level determining section 13,that is changed by the severity modification circuit 30 to a modifiedfinal protection level B. If the switch position is P_(C), then theleast severe value of the modified final protection level is changed toC. If the switch position is P_(D), then the least severe value of themodified final protection level is changed to D, and if the switchposition is P_(E), then the modified final protection level is fixed asE.

The same is true for each of the apparatus protection level values 2, 3and 4, as illustrated in diagrams (B), (C) and (D) in FIG. 16, whichcorrespond to the second, third and fourth columns in FIG. 2respectively.

It will be apparent that the severity modification circuit 30 can beeasily configured using a logic circuit, which implements a simplealgorithm in accordance with the setting of the severity modificationsetting switch 31, i.e. the algorithm would begin:

[If the severity modification switch 31 is set at P_(A), transfer theprotection level value established by the final protection leveldetermining section 13 directly to the protection control signalgenerating section 14 a, as the final protection level.

If the severity modification switch 31 is set at P_(B), and if theprotection level value established by the final protection leveldetermining section 13 is level A, change that to level B and transferto the protection control signal generating section 14 a as the(modified) final protection level. Otherwise, transfer the protectionlevel value produced from the final protection level determining section13 unchanged, as the final protection level.

If the severity modification switch 31 is set at P_(C), and if theprotection level established by the final protection level determiningsection 13 is level A or level B, change to level C, and transfer to theprotection control signal generating section 14 a as the finalprotection level. Otherwise, transfer the protection level establishedby the final protection level determining section 13 unchanged, as thefinal protection level . . . ], and so on.

Thus with this embodiment, if the severity modification setting switch31 is set to its least severe position (P_(A)), then the relationshippattern between combinations of the medium protection level andreproduction apparatus protection level values will be as shown in FIG.2. If the severity modification setting switch 31 is set to the mostsevere position (P_(E)), then the relationship pattern will be such thatthe final protection level will always be the highest level, i.e. levelE. As the severity modification setting switch 31 is successivelychanged from positions P_(A) to P_(E,) the least severe degree ofreproduction restriction (within the range of possible degrees ofrestriction which can be set by the final protection level) is increasedto a more severe degree, by successive steps.

For example if the apparatus protection level is 2 and the mediumprotection level is 4, then the final protection level will be B.However by altering the setting of the severity modification settingswitch 31, the user can change the final protection level to a highervalue, in the range B to E. Hence with this embodiment, althoughprotection level values can be specified by the manufacturer orcopyright owner of the recording medium, and by the manufacturer orseller of the reproduction apparatus, the final degree of protection canbe determined by the person who is in charge of the reproductionapparatus. Such a feature is highly useful.

As can be understood from the above description of embodiments, theinvention enables a final protection level to be established, forcontrolling reproduction of recorded or transmitted video or audiosignals, with that final protection level being determined based on acombination of protection levels which are respectively separatelyestablished by the manufacturer or copyright owner of recorded signals(or broadcaster of transmitted signals, or copyright owner oftransmitted signal) and by the manufacturer or seller of thereproduction apparatus. The final protection level can be applied suchas to achieve extremely precise protection of reproduction, whereby forexample specific frames of a video signal, and/or specific regionswithin a frame, can be protected by restricting reproduction, with thedegree of restriction being variable in a stepwise manner. The inventioncan at the same time provide corresponding protection of an audio signalwhich is being reproduced in conjunction with a video signal.

Although the invention has been described in the above with reference toa CD player apparatus, it will be understood that the invention is notlimited in any way to such an apparatus, and is in general applicable toreproduction protection in any type of apparatus which reproduces arecorded or transmitted video and/or audio signal.

I claim:
 1. A transmission method for operating on information which istransmitted through a medium and comprises main data which are to betransmitted, the method comprising the steps of: detecting protectiondata which are also transmitted through said medium; generatingadditional protection data which comprise at least first additionalprotection data and second additional protection data, wherein saidfirst additional protection data are specific to a region or a countryin which said main data are to be transmitted, and are unmodifiable by arecipient of said transmitted main data, and wherein said secondadditional protection data can be modified by the recipient toselectively define a plurality of protection levels including at leasttwo levels which are respectively specific to adults and to children;defining a protection level based on said protection data and on saidadditional protection data, in combination; and executing transmissionof said main data in accordance with said protection level, wherein thecombination of said protection data and said first additional protectiondata specifies that said main data are transmitted either in theirentirety or not at all, and the combination of said protection data andsaid second additional protection data specifies that said main data aretransmitted either in their entirety, partially, or not at all.
 2. Thetransmission method as recited in claim 1, wherein said medium transfersboth said protection data and said main data in an identical form. 3.The transmission method as recited in claim 1, further comprising thestep of transmitting both said protection data and said main datathrough said medium in an identical form.
 4. The transmission method asrecited in claim 1, wherein said step of executing transmission of saidmain data comprises: transmitting said main data either in theirentirety or not at all, in accordance with said combination of saidprotection data and said first additional protection data, andtransmitting said main data in their entirety, partially, or not at all,in accordance with said combination of said protection data and saidsecond additional protection data.